Systems and methods for tuning filters

ABSTRACT

Methods, systems and apparatus for filter design, analysis and adjustment are provided. Various embodiments may include, for example, methods, systems and apparatus for electric signal filter tuning. Embodiments may also include design techniques for planar electric signal (e.g., RF signals) filter tuning. In at least an embodiment of the present invention a technique for filter tuning is provided which may include parameter extraction, optimization and tuning recipes techniques that may require only a single permanent filter tuning. In at least another embodiment a system and method of filter design, analysis and adjustment according to the present invention includes use of tuning that may be set using a mechanical scribing tool or a laser trimming device. In at least one other embodiment, a filter tuning technique may be provided and include providing trimming tabs on a resonator edge that may be disconnected or trimmed for filter tuning.

STATEMENT OF GOVERNMENT INTEREST

The invention provided herein was, at least in part, supported by theTotally Agile RF Sensor Systems, issued by DARPA/CMD under Contract No.MDA972-00-C-0010. The U.S. Government has a paid-up license in thisinvention and the right in limited circumstances to require the patentowner to license it to others on reasonable terms as provided for by theterms of Contract No. MDA972-00-C-0010 awarded by Defense AdvancedResearch Projects Agency, Defense Sciences Office, Order No. J607(DARPA/CMD).

This application claims the benefit of U.S. Provisional Application No.60/632,084, filed Nov. 30, 2004, the entire disclosure of which ishereby incorporated by reference as if set forth fully herein.

BACKGROUND

1. Field of the Invention

The present invention relates to the field of filter analysis and designand, more specifically, to systems and methods relating to tuningfilters.

2. Description of Related Art

The past few decades have seen considerable advancement in electronicsand wireless communications. The continued development and advancementof more highly dense integrated circuits at low cost has enabled aplethora of mobile devices, and particularly wireless mobile devices, tobecome prevalent around the world to the point of being ubiquitous.Mobile devices having wireless capability and found throughout the worldtoday include, for example, mobile telephones, personal digitalassistants (PDAs), laptop computers, global position sensor (GPS)devices. These devices typically operate in the radio frequency (RF) andmicrowave wireless signal frequency ranges.

The electronics for communicating at RF and microwave frequency requirestransmitters and receivers with electric signal filters to assist inproducing and/or discriminating between wanted signals and unwantedsignals. However, it is difficult to build an electric signal filter forwireless communication that has ability to discriminate between wantedand unwanted signals as well as desired. Therefore, the electric signalfilters are tuned after being made or manufactured, so that they arebetter at producing and/or discriminating between wanted and unwantedsignal frequencies.

Electric filters for wireless communication include, for example, cavitytype filters and planar type filters. Electronic filters such as theplanar filter may include a series of resonators coupled together. Highperformance planar filters, for example high temperature superconductorfilters (HTS), have been developed to provide extremely accuratefiltering to improve the quality of wireless communications,particularly in areas having a high density of wireless devices or wherethe RF or microwave signals may not propogate well. See, for example,U.S. patent application Ser. No. 10/944,339 “Stripline Filter UtilizingOne or More Inter-resonator Coupling Members” which is herebyincorporated herein by reference for all purposes.

Planar filters are usually patterned on high dielectric constantsubstrates and designed to be very compact in size. Using the preciselithography techniques developed for semiconductor processing, couplingsthat are well repeatable within in acceptable range can be produced.Unlike cavity filters, planar filters do not generally require tuning ofthe couplings because the filter response is less sensitive to couplingvariations than resonant frequency variations. However, substratethickness variations and/or process variations such as etchingconditions are likely to cause unacceptable resonant frequencyvariations of planar filters, and thus require tuning of planar filters.

Several tuning techniques have been used for planar filters, for examplehigh performance superconductor filters, have been developed.Maintaining high-performance in the filter design stage or inmanufacturing requires a stable tuning process. There are two mainapproaches to planar filter tuning. The first approach, mechanicaltuning, is widely used in the industry. Filters may be tunedmechanically by moving elements such as dielectric rods or conductivetips within the electromagnetic field near resonators. For example,tuning screws may be used to move the dielectric rods or conductive tipsup and down over the resonators. For superconductor filters, sapphirerods or superconductor-coated tips may be used on the tuning screws.Sapphire rods may placed at high electromagnetic field area overresonators and tune resonant frequency by changing shunt capacitance toground. Superconductive tips can be used for magnetic and/or electricfield tuning, but usually they are applied to the electromagnetic fieldbecause it can tune more effectively. The tip changes theelectromagnetic field surrounding the resonator(s) and varies inductanceof resonator(s). One exemplary method of providing mechanical tuning isdescribed in U.S. Pat. No. 5,968,876 by Sochor, which is herebyincorporated by reference herein for all purposes.

One advantage of the mechanical tuning approaches is reversibility.Filters are tuned through a trial and error process by moving the tuningelements or screws up and down. Later on, tuning still can be adjustedif it is necessary. One disadvantage of mechanical tuning is that thetuning elements or screws can potentially impact the resonantfrequencies of other resonators or inter-resonator couplings when theyare applied, especially when they are placed close to the circuit. Inreality, that happens often. The variation in coupling ultimately limitsthe filter's tuning range. This effect can be minimized by taking itinto account during filter design. Designers may arrange resonatorstuning locations away from each other and away from the couplings toavoid that impact. This concern and approach limits freedom of design ofplanar filters. There are other issues that may be caused by havingmechanical part. For example, metallic or dielectric flakes may dropfrom mechanical elements or screws during and after tuning. These flakesmay affect the filter Q-factor and also change tuning as they are freeto move around on the circuit. The tuning elements also need to be fixedor locked in location after the tuning is finished to keep the filter'sperformance constant.

The second approach is done by processing and does not need mechanicalparts. A couple of methods, such as laser trimming a portion of thefilter trace or depositing a thin dielectric layer over the filter tracehave been reported. One exemplary laser trimming technique is shown inthe article by Parker, Ellis and Humphreys, Tuning SuperconductingMicrowave Filters By Laser Trimming by Goodyear, IEEE MTT-S Digest,2002, which is hereby incorporated herein by reference for all purposes.One exemplary dielectric deposition technique is described in thearticle by Tsuzuki, Suzuki, and Sakakibara, Superconducting Filter forIMT-2000 Band, IEEE Transactions on Microwave Theory and Techniques,Vol. 48, No. 12, December 2000, which is hereby incorporated herein byreference for all purposes. These approaches will result in permanenttuning changes, and should not change once they are set. Thus, there isno chance to retune or readjust the filter. Hence, tuning must be donevery carefully so that the filter is not permanently ruined.

In general, the second approach is preferable to the first approach,even though the first approach is predominantly used. However, there aretwo major issues that must be resolved in order to realize the secondapproach. First, a reproducible tuning process must be developed.Second, a robust method that provides a tuning recipe is needed. Bothmust be very accurate since the tuning is generally not reversible. Itwould be beneficial if a filter design may be provided that isinsensitive to trimming accuracy so as to often tune filters accurately.The present invention provides a number of approaches to filter tuningand design which meet these requirements.

SUMMARY

The present invention is directed generally to providing methods,systems and apparatus for filter design, analysis and/or adjustment.More specifically, embodiments may include systems, methods, andapparatus relating to electronic filter design and tuning.

Such embodiments may include, for example, a plurality of steps thatwill result in improved filter tuning. A filter may be operated at anexpected operating temperature to determine various initial orpre-tuning performance characteristics. Parameter extraction may then beperformed by, for example a network analyzer and a computer. Forexample, measured S-parameter response (e.g. return loss) may be used todetermine various parameters associated with the filter. Next, filterresponse may be optimized by, for example, a computer. In variousembodiments, the couplings (e.g., between resonators of a filter) may bekept constant and the frequency may be adjusted to optimize the filter'sS-parameter response. Then a difference between the extracted filtercharacteristics and the optimized filter characteristics may bedetermined and used to provide a tuning recipe. The filter may then betuned according to the tuning recipe. In various embodiments this tuningmay be done by cutting or trimming a portion of the filter, a tuningfork coupled to a portion of the filter, and/or a trimming tab coupledto a portion of the filter. Once the filter has been tuned, it may bechecked. For example, the filter may again be operated at its operatingtemperature and measured to determine the filter's new performancecharacteristics. If the new tuned performance characteristics areacceptable, the filter may be packaged for operation. If the newperformance characteristics are not acceptable, the filter may be tunedagain or scrapped. However, it should be noted that the presentinvention enables most filters may be properly tuned in the firsttuning.

In at least one embodiment, the parameter extraction method may be usedto diagnose the “turn on” state of the filter. The cross coupling(s) ofvarious resonators of a multi-resonator filter may be treated asconstants during extraction. In various embodiments, only dominantparasitic couplings along with main couplings may be utilized to obtainmore accurate result. Further, multiple data sets may be utilized inorder to avoid local minimum solutions caused by the existence ofparasitic coupling(s) and/or a “dirty window” (e.g., connectors,bondings, transmission lines, cables, etc., needed to connect the filterto the instrumentation used to measure the filter performance). Then anoptimization of the filter response may be performed based on thediagnosis information from parameter extraction. For example, the returnloss may be optimized allowing slightly narrower bandwidth by usingextracted couplings, but changing only the resonators. Further, therejection response may be optimized as well by allowing the return lossto be slightly degraded.

In at least one embodiment, the invention may include a design techniqueand filter design for high-performance planar filters. The techniqueprovides one or more tuning elements that enable filter tuning by, forexample, hand scribing, and a parameter extraction based technique todetermine what should be scribed. In a multi-resonator planar filter,each resonator may have a tuning element, for example a tuning fork,that provides shunt capacitance to ground. The tuning fork may becoupled to the resonator by means of a series capacitor or connecteddirectly to the resonator. However, sensitivity to error in scribing isdecreased if the tuning fork(s) is connected directly to the resonator.The series capacitor can be designed to reduce the tuning sensitivity toapproximately 10% of what would be seen if the tuning fork was directlyconnected to the resonator. This reduced sensitivity enables tuning byhand, e.g. with a mechanical device such as a diamond scribe pen. Thehand scribing may be performed with a diamond scribe pen under amicroscope. Alternate means of scribing the tuning fork, such as a laserscribing tool may also be employed. In any case, the resonator may betuned by physically disconnecting (e.g., scribing) part of the tuningfork or shunt capacitor. For accuracy and ease of tuning, the tuningfork may also include a scale and/or numbering. Further, differentcapacitance tuning forks may be provided to give both course and finetuning. A parameter extraction based technique may be used to diagnosethe filter couplings and resonant frequencies, and to provide a recipefor scribing the tuning forks. As such, a filter design is provided thatrealizes very accurate tuning without requiring any expensive tools.However, in one variation, a laser trimming machine may be used tophysically disconnecting a portion of the tuning fork or shuntcapacitor.

In at least one other embodiment, the invention may include a procedurefor tuning a planar filter including planar tuning elements. A planarfilter including a planar tuning element may be provided. Various filtercharacteristics, for example, the frequency and return loss may beanalyzed to determine if tuning is needed. If tuning is needed,calculations are performed to determine how to correctly tune the planarfilter. For example, filter response optimization may be performed and atuning recipe may be developed. Then, one or more tuning elements may beadjusted so that at least a portion of the filter is correctly tuned.

In at least one other embodiment, the invention may include providingone or more trimming tabs on a resonator edge that may be, for example,trimmed (i.e. disconnected from the circuit) for filter tuning. Thetrimming tabs may have discrete values that shift a resonant frequencyof the filter by different known amounts, and the amounts may beconfigured in a binary progression. For example, the filter may havefour trimming tabs on each resonator that can shift resonant frequencyin a binary progression such as 800 kHz, 400 kHz, 200 kHz and 100 kHz.Additional tabs may be provided for coarse and/or fine tuning such as a1500 kHz tab and/or additional 100 kHz tabs. The filter may be tested(e.g., at operating temperature) to determine its characteristics andparameter extraction may be performed. Then parameter optimization maybe performed to determine, for example, the frequency shift for eachresonator in the filter. From this information a tuning recipe may begenerated indicating which of the trimming tabs should be disconnectedor trimmed from the resonator(s) edge(s) so as to produce a properlytuned filter. The trimming tabs may be severed from the resonator(s)using a laser or mechanical scribing apparatus.

The methods, systems and apparatus provided herein may be particularlywell suited for tuning planar filters that may be used in RF andmicrowave applications. In various embodiments, the planar filters bemade of a high temperature superconductor material (HTS).

The parameter extraction and optimization techniques of the presentinvention are not limited to the filter designs used our developmentsuch as trimming tab resonator and tuning fork resonator filter designs.These techniques are also applicable to mechanical tuning such asdielectric tuning filters and HTS tip tuning filters. However, asdescribed herein they are particularly effective for trimming tabresonator and tuning fork resonator filter designs.

Some of the advantages of the processing approaches provided herein are(1) filters that have simpler structure and lower cost because there areno mechanical parts required for tuning, (2) filters that are morereliable because the tuning is permanent, and (3) filters is morefreedom of design layout due to the lack of mechanical tuning elementsor screws that need to be taken into consideration during the designlayout of planar filters.

Still further aspects included for various embodiments are apparent toone skilled in the art based on the study of the following disclosureand the accompanying drawings thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The utility, objects, features and advantages of the invention will bereadily appreciated and understood from consideration of the followingdetailed description of the embodiments of this invention, when takenwith the accompanying drawings, in which same numbered elements areidentical and:

FIG. 1 is a flowchart of a method of tuning a filter according to atleast one embodiment;

FIG. 2 is a block diagram illustrating a system for filter tuningaccording to an embodiment;

FIG. 3 is a circuit diagram of a filter and tuning element according toan embodiment;

FIG. 4 is a side view of a planar filter device with tuning elementaccording to at least one embodiment;

FIG. 5 is a top view layout of a planar filter device with tuningelements according to at least one embodiment;

FIG. 6 is a graph of the tuning range and sensitivity for one of thetuning forks shown in FIG. 5, according to at least one embodiment;

FIG. 7 is a graph of the tuning range for both of the tuning forks shownin FIG. 5, according to at least one embodiment;

FIG. 8 is flowchart of a method of tuning a filter according to at leastone embodiment;

FIG. 9 is a top view layout of a multi-resonator planar filter devicewith tuning fork tuning elements according to at least one embodiment;

FIG. 10 is a graph of the initial measurement data before tuning for thefilter shown in FIG. 9, according to at least one embodiment;

FIG. 11 is an extracted coupling matrix for the filter shown in FIG. 9,according to at least one embodiment;

FIG. 12 is a graph of the extracted and optimized frequencies for eachof the resonators in the filter shown in FIG. 9, according to at leastone embodiment;

FIG. 13 is a graph of the initial measured and optimized return loss forthe filter shown in FIG. 9, according to at least one embodiment;

FIG. 14 is a table of the recipe for tuning resonators 1-10 for filtershown in FIG. 9, according to at least one embodiment;

FIG. 15 is a diagram showing actual scribe lines on the tuning forks ofresonators 7, 8 and 9, and the related portion of the recipe table forthe filter shown in FIG. 9, according to at least one embodiment;

FIG. 16 is a graph of tuned and optimized return loss for the filtershown in FIG. 9, according to at least one embodiment;

FIG. 17 is a graph of the measurement data after tuning of the filtershown in FIG. 9, according to at least one embodiment;

FIG. 18 is a top view layout of a multi-resonator planar filter devicewith trimming tab tuning elements according to at least one embodiment;

FIG. 19 is a portion of the top view layout of a multi-resonator planarfilter device shown in FIG. 18, enlarged to better show the trimming tabtuning elements, according to at least one embodiment;

FIG. 20 is a diagram of a physical layout for a typical non-ideal filtertest environment, according to at least one embodiment;

FIG. 21 is a block diagram of a equivalent circuit for the layout inFIG. 20, according to at least one embodiment; and

FIG. 22 is a block diagram for a further simplified equivalent circuitmodel for the non-ideal filter environment, according to at least oneembodiment.

DETAILED DESCRIPTION

The present invention is directed generally to filter design, analysisand adjustment. Various embodiments may include, for example, methods,systems and apparatus for electric filter tuning. Embodiments may alsoinclude design techniques for planar electric filter tuning. Themethods, systems and apparatus of the present invention may beparticularly well suited for tuning planar filters that may be used inRF and microwave applications. In various embodiments, the planarfilters be made of, for example, a high temperature superconductor (HTS)materials such as YBa₂Cu₃O_(7-δ) (YBCO). Embodiments of the presentinvention may also include parameter extraction, optimization and tuningrecipes techniques. These techniques are not limited to applicationswith the filter designs used herein, such as trimming tab resonator andtuning fork resonator filter designs. These techniques may alsoapplicable be applicable to mechanical tuning such as dielectric tuningfilters and HTS tip tuning filters. However, the techniques describedherein are particularly effective for trimming tab resonator and tuningfork resonator filter designs.

In at least an embodiment of the present invention a technique forfilter tuning is provided which may include parameter extraction,optimization and tuning recipes techniques that may require only asingle permanent filter tuning. In at least another embodiment a systemand method of filter design, analysis and adjustment according to thepresent invention includes use of tuning that may be set using amechanical scribing tool or a laser trimming device. In at least oneother embodiment, a filter tuning technique may be provided and includeproviding trimming tabs on a resonator edge that may be disconnected ortrimmed for filter tuning.

Referring to FIG. 1, a method for tuning a filter is provided. Thisembodiment may include a plurality of steps 110-140 that will result inimproved filter tuning. At 110, a filter may be operated at an expectedoperating temperature to determine various initial or pre-tuningperformance characteristics. For example, an HTS filter may be operatedat 77 degrees K and measurements taken. At 115, parameter extraction maythen be performed by, for example a network analyzer (shown as item 235in FIG. 2). For example, measured S-parameter response (e.g. returnloss) may be used to determine various parameters associated with thefilter. Next, at 120, filter response may be optimized by, for example,a computer (shown as item 205 in FIG. 2). In various embodiments, thecouplings (e.g., between resonators of a filter) may be kept constantand the frequency may be adjusted to optimize the filter's S-parameterresponse. Then at 125 a difference between the extracted filtercharacteristics and the optimized filter characteristics may bedetermined and used to provide a tuning recipe. At 130, the filter maythen be tuned according to the tuning recipe. In various embodimentsthis tuning may be done by, for example, cutting or trimming a portionof the filter, a tuning fork coupled to a portion of the filter, and/ora trimming tab coupled to a portion of the filter. Once the filter hasbeen tuned, it may be checked. For example, at 135 the filter may againbe operated at its operating temperature and measured to determine thefilter's new performance characteristics. If the new tuned performancecharacteristics such as frequency response and/or S-parameter responseare acceptable, the filter may be packaged for operation. The methodprovided herein will often result in acceptable filter performance aftera single iteration of the aforementioned tuning procedure, and at 145the method of tuning will end. However, if at 140 the new performancecharacteristics are not acceptable, the filter may be tuned again orscraped. It should be noted that the use of the parameter extraction,filter performance optimization, and tuning recipe procedure providedherein enables most filters to be properly tuned in the first tuning.

Referring to FIG. 2, a block diagram illustrating a system for filtertuning according to an embodiment of the present invention is provided.In this example, a computer 205 may coupled to a network analyzer 235and the network analyzer 235 may be coupled to a filter to be tested andtuned. The filter 240 may be coupled to the network analyzer 235 usingRF cables. The computer 205 may be a personal computer (PC) or any othertype of computer capable of performing the analysis and computationsnecessary for filter tuning. The computer 205 may include a controllerand processor 210 and a memory 215. The memory may contain parameterextraction 220, filter response optimization 225 and tuning recipe 230information. In operation, the network analyzer 235 may performparameter extraction and the parameter extraction information 220 may bestored in memory 215. The computer 205 controller and processor 210 maythen use a program to generate filter response optimization information225 that is stored in memory 215. Next, the controller and processor 210may use a program to generate tuning recipe information 230 that mayassist an operator or automated tuning system to tune the filter 240 todesired performance characteristics. In various embodiments, the filter240 may be set to a device operating temperature. For example, acryostat (not shown) may be used in which the filter is disposed so asto reduce the temperature of an HTS filter to operating temperature of,for example, 77K.

Referring now to FIG. 3, a circuit diagram for an equivalent circuit ofan exemplary filter and tuning element are provided, according to anembodiment of the present invention. In this example, a filter resonatormay be modeled simply ad a capacitor C₀ 305 and inductor L 310. Thetuning element is modeled as a variable shunt capacitor C_(s) 320 and iscoupled to the resonator (305 and 310) by a gap capacitor C_(g).However, in one variation the tuning element is variable shunt capacitorC_(s) 320 may be directly connected to the resonator (305 and 310). Theresonator may be tuned by changing shunt capacitor to ground c_(s) 320.

Referring to FIG. 4, a side view of a planar filter device with tuningelement is provided, according to at least one embodiment. In thisexample, a filter structure 405 may be formed by forming one or moreresonators and tuning devices 420 on a substrate that may include adielectric substrate or material 410 and a ground plane 415. Typically,the resonators and tuning devices 420 and ground plane 415 are made froma conductive material such as a gold or copper. In the case of microwavefilter structure, resonators and tuning devices 420 and ground plane 415may be made from an high temperature superconductor (HTS) materials suchas YBa₂Cu₃O_(7-δ) (YBCO).

Referring to FIG. 5, a top view layout of a planar filter device withtuning elements is provided, according to at least one embodiment. FIG.5 shows an exemplary resonator 505 formed with spiral-in and spiral-out(SISO) shape half-wavelength structure that may be represented using thecircuit diagram of FIG. 3. A complete filter may include multipleresonators 505, for example, eight or ten resonators 505 in series. TheSISO trace 505 may be made of metal as described for the resonators andtuning devices 420 shown in FIG. 4. Some details for such devices may befound in, for example, the article by Gregory L. Hey-Shipton, EfficientComputer Design Of Compact Planar Band-pass Filters Using ElectricallyShort Multiple Coupled Lines,” 1999 IEEE MTT-S Int. Microwave Symp.Dig., June 1999, which is hereby incorporated by reference for allpurposes. The invention should not be construed as being limited to onlySISO and SISO-like resonators, but is broadly applicable to a wide rangeof resonator types such as those described in U.S. Pat. No. 6,895,262titled High Temperature Superconducting Structures and Methods for HighQ, Reduced Intermodulation Structures, U.S. patent application Ser. No.10/480,743 titled Resonator and Filter Comprising the Same, U.S. patentapplication Ser. No. 10/391,667 titled Narrow-Band Filters with Zig-ZagHairpin Resonator and the article Highly-SelectiveElectronically-Tunable Cryogenic Filters Using Monolithic,Discretely-Switchable MEMS Capacitor Arrays, E. M. Prophet, J. Musolf,B. F. Zuck, S. Jimenez, K. E. Kihlstrom and B. A. Willemsen, IEEETransactions on Applied. Superconductivity, 15, 956-959 (2005), whichare all references hereby incorporated by reference for all purposes.The device 500 in this example may be named a “Tuning Fork Resonator”design and be tuned using, for example, hand scribing or laser scribing.One or more “Tuning Fork” tuning element(s) 520 and 525 made of metalmaterial may be connected to the resonator 505 through a seriesinter-digitated capacitor c_(g) 315 via structure 515, at one end of theresonator. Although two tuning fork elements 520 and 525 are shownherein, one or more tuning forks may also be used depending on thetuning range and tuning resolution required. The tuning fork element(s)520 and 525 may be electrically floating from the resonator 505.Further, tuning fork element(s) 520 and 525 may include scales 530 and535, respectively, to provide ease of scribing. The scale may be relatedto a tuning recipe (described in more detail below). Note, that at theother end of the resonator 505 a structure 510 enabling interdigitatedcoupling may also be included. As will be discussed in more detailbelow, structure 510 may be used for coupling together two or moreresonators 505 included in a planar filter.

Frequency tuning of the resonator 505 may be implemented by scribingaway portions of one or more of the floating tuning fork(s), for exampletuning fork 530. This has the effect of reducing the shunt capacitancec_(s) 320 of the floating part (between 315 and 320), as shown inequivalent circuit in FIG. 3. In this case, the total capacitance of aresonator can be described as:

C₀− > C = C₀ + H $H \equiv \frac{C_{g}C_{s}}{C_{g} + C_{s}}$Original frequency f₀ may change to f by including the tuning forkstructure.

${f_{0}->f} = {{\frac{1}{2\;\pi\sqrt{L\left( {C_{0} + H} \right)}} \cong {f_{0}\left( {1 - {\frac{1}{2}\frac{H}{C_{0}}}} \right)}} = {f_{0} + {\Delta\; f}}}$Sensitivity of frequency shift can be evaluated by derivative of Δf byc_(s):

$\frac{{\mathbb{d}\Delta}\; f}{\mathbb{d}C_{s}} = {{- \frac{f_{0}}{2\; C_{0}}}\frac{\mathbb{d}H}{\mathbb{d}C_{s}}}$The sensitivity factor

$\frac{\mathbb{d}H}{\mathbb{d}C_{s}} = \frac{C_{g}^{2}}{\left( {C_{g} + C_{s}} \right)^{2}}$represents sensitivity ratio to the case when the fork is directlyconnected to resonator and a part of resonator is scribed without anydecoupling structure.

FIG. 6 shows frequency shift and the sensitivity factor to scribedlength L calculated for the example shown in FIG. 5, tuning fork element520. The calculations may be done using a computer program, for exampleMomentum provided by Agilent Technology. As shown by curve 610, thisparticular exemplary tuning fork element 520 may be designed to be ableto tune by approximately 1 MHz as maximum delta when the fork is scribedat approximately 2 mm, which is almost the full length of the tuningfork. The sensitivity factor varies from approximately 0.05 to 0.3 overthe range shown in FIG. 6, as indicated by curve 605. Thus, as indicatedby curve 610, in this example the sensitivity is approximately 12 kHz/50μm at L=0 and 46 kHz/50 μm at L=2.0 mm. If in another embodiment, thetuning fork 520 may be directly connected to the resonator 505 and thefrequency shift 610 amount may be approximately 9.2 MHz when the tuningfork 520 is scribed at 2.0 mm. This may be defined as a fine tuningtuning fork 520, relative to tuning fork 525. Further, in the case ofthe tuning fork 520 being directly connected to the resonator 505, thesensitivity obtained from curve 610 may be approximately 230 kHz/50 μmand that would be constant over the range (straight line), unlike theexample where the tuning fork is decoupled as shown in the figures. Theuse of capacitive coupling for the tuning fork(s) 520 and 525 providesfor reduced sensitivity and may facilitate use of less accuratemechanical scribing techniques for tuning the resonator(s) 505. Forexample, in this case the design is capable of being tuned using handscribing using a mechanical scribe device. The maximum sensitivityfactor H in the tuning range provided in FIG. 6 may be less than 30% ofan embodiment where the tuning element 520 is connected directly to theresonator 505. In one embodiment, for example, a 50 (+/−25) μm precisionmay be achieve using a diamond scribe pen under a microscope. In thiscase it may be possible to realize, even for an inexperienced persontuning the device, a single tuning fork 520 being tune and resulting inthe tuning of the resonator 505 within approximately 50 kHz precisionover the 1 MHz range. Sensitivity and tuning range can be adjusted bychanging series capacitance c_(g) 315 between resonator 505 and thetuning element(s) 520 and 525. Tuning becomes less sensitive bydecreasing the series capacitance c_(g) 315, but it may also need moreshunt capacitance to ground C_(s) 320 to keep the same amount of tuningrange, which may result in longer tuning fork. In any case, the variousdesign parameters should be determined for needed tuning range,acceptable sensitivity and realizable physical size of the tuning fork.

FIG. 7 is a graph of the tuning range and frequency shift for bothtuning forks 520 and 525 shown in FIG. 5, according to at least oneembodiment. In this graph, the scale is larger to accommodate curve 710for the more course tuning fork 525, due to additional surface area andshunt capacitive coupling. The second tuning fork 525 may provideapproximately 2.5 MHz of tuning. The tuning capability of tuning fork525 of 2.5 MHz may be added to the first tuning fork 520 capability of 1MHz, so as to expand the total tuning range to 3.5 MHz. However, thesensitivity of the second tuning fork 525 is not as good as thesensitivity of the first tuning fork 520, because of its wider tuningrange. In one variation, if 2.0 MHz of tuning was adequate for tuningmost of the resonators 505, we could have used two of the same size andtype tuning forks and preserved the tuning sensitivity. As noted above,and described below in more detail, scales 530 and 535 and numbers(shown below) may be marked along the forks to make hand scribing moreeasy.

FIG. 8 is flowchart of an exemplary method of tuning a filter accordingto at least one embodiment. At 810, a planar filter may be provide fortuning. This planar filter may be manufactured according to processingand design techniques well known to those skilled in the art and thetechniques described herein. The planar filter may include one or moreresonators (e.g., resonator 505). At 815, a planar tuning element (e.g.,tuning forks 520 and/or 525) may be provided and coupled or connected tothe filter so as to enable tuning of the filter. At 820, the filterassembly may be analyzed and various filter characteristics measured soas to determine if the filter needs to be tuned to a desired filterperformance. These measurements may be provided by a network analyzer orother measurement device. Filter performance parameters may beextracted. The desired filter performance characteristics may beprogrammed into or derived using, for example, a computer. This mayinclude performing filter response optimization. At 825, the desiredpredetermined filter performance characteristics may be compared to themeasured filter characteristics to determine if filter tuning is needed.If filter tuning is needed, then at 830 it is calculated how tocorrectly tune the planar filter. In this case, a filter tuning recipemay be generated. Than at 835, one of more planar tuning elements may beadjusted, by for example scribing, so that at least one portion orresonator of the filter is correctly tuned. Once tuned, the filterperformance may again be analyzed to determine if any further tuning isneeded in steps 820 and 825. Alternatively, the filter may be packagedfor use without confirming performance.

Referring to FIG. 9, a top view layout of one exemplary filter designincluding a multi-resonator planar filter device with two tuning forktuning elements per resonator is provided, according to at least oneembodiment. As an exemplary filter design example, an 800 MHz cellularB-band filter 900 is shown from a top view. The filter layout may be,for example, a 10-pole AMPS-B filter 900. As such, ten resonators, 901through 910 (901-910), may be provided in series and are cross-coupledtogether. The filter chip dimension may be, for example, a 34 mm by 18mm so that two filters may be fabricated on, for example, a 2-inch MgOwafer. The design pass band may be designed to be from 834.8 MHz to849.7 MHz with a return loss of 22 dB. Of course, the filter 900 may bedesigned for a different desired pass band and return loss or as a bandgap filter or any other type of filter typical in the art. In thisexample, the filter 900 may include three quadruplet cross couplings,915, 916, and 917, that may produce three transmission zeros at eachrejection side. Those values may be designed such that three bounce backpeak levels may occur at 70 dB. The cross couplings 915, 916, and 917may be implemented at one side of the resonators array (e.g., the topside) by additional transmission lines and may be capacitively coupledto resonators 901-910 via coupling elements 510. Tuning forks 921Athrough 930B may be hung at the other side of the resonators array901-910. Although two tuning forks are couple to each resonator in thisexample, one skilled in the art would understand that one tuning fork ormore that two tuning forks may be attached to each resonator. In thisexample, two tuning forks (e.g., 921A and 921B) that may give differenttuning ranges are coupled to a respective resonator hung at the bottomof each resonator. As described above with respect to resonator 505,numbers and scales may be provided beside tuning forks allows handscribing easier. The numbers 1-9 and X (i.e., 10) may be used to make iteasier to identify the location of a particular resonator during scribetuning. Further, the scales along the side of the tuning forks 921A-930Bcan make it easier to cut the tuning forks in the proper location.

The cross couplings parts 915-917 and the tuning forks 921A-930B may bephysically separated from main coupling stream that is carried outthrough center part along the direction from input 911 to output 912.Furthermore, the main couplings between the adjacent resonators (forexample 901 to 902 or 902 to 903 etc. . . . ) are predominantlyinductive, in contrast with the coupling via cross couplings 915-917 andthe couplings to tuning forks 921A-930B, which are capacitive. Thefilter is designed to minimize interference between those threedifferent kinds of couplings (the main couplings, the cross couplingsand the tuning fork couplings). As described above with reference to theresonator 505, the “A” designated tuning forks 921A-930A may be used forfine tuning the resonators 901-910 and the “B” designated tuning forks921B-930B may be used for course tuning the resonators 901-910. Thetuning procedure for filter 900 will be described in detail below.

In one variation, the tuning process for filter 900 may be as follows.The filter 900 may be measured with a network analyzer (e.g., 235) andthe data may be taken and saved in a memory (e.g., 215) of a computer(e.g., 205). The data may then be analyzed using a computer program viaa controller/processor (e.g., 210). The computer program may proceed asfollows. First, the electrical structure of the filter may be known,such as the number of resonators 901-910 and cross coupling structure915-917, but a numbers of factors such as the resonant frequencies ofresonators 901-910 and the couplings between the main portion of theresonators 901-910 may not be known. Once you know the numbers for thefrequencies of resonators 901-910 and the couplings between the mainportion of the resonators 901-910, you may then determine what's goodand what's wrong on the filter 900 and you may be able to fix it. Thecomputer program may then extract those numbers for you from measurementdata. For example, for the B-band filter 900 having 10 resonators901-910 and three cross coupling structures 915-917. In this example,mathematically, a 10-by-10 matrix and a couple of additional parametersmay be used to represent the filter 900 and its environment. Thoseparameters may represent the filter's characteristics, such as resonantfrequencies (diagonal elements 1105) and couplings (main couplings 1110,desired cross couplings 1120, and undesired parastic couplings 1115).The additional parameters R1 and R10 describe the filter terminations,and thus its environment. By varying those parameters, the computerprogram may try to fit a computed characteristic curve into ameasurement characteristic curve. If the fitting succeeded, theparameters determined by the computer program are the parameters of themeasured filter 900. Once the filter's characteristics are extractedthrough this iterative process, the next step is the tuning. In oneexample, coupling values may be assumed to be constant and frequency maybe tuned by using the tuning elements such as tuning forks 921A-930B.After the parameter extraction process, the matrix shown in FIG. 11 maybe generated that contains all the information about the filter. Then,rather than changing (tuning) all the parameters in order to optimizefilter response you only need to change the resonator frequencies, i.e.the diagonal elements of the matrix. This is possible because all theoff diagonal elements are reasonably stable from run to run infabrication due to accurate photolithography technology. Theoff-diagonal elements (coupling values) have already been establishedthrough a couple of re-design iterations before the final filter designis complete, so the couplings are typically well designed and reasonablystable, from one filter to another and across different processing andfabrication lots. However, the resonator frequencies usually show morevariation in fabrication and may then need to be corrected (tuned). Byvarying the frequencies and keeping the couplings the same from theextracted coupling values, the return loss and/or insertion loss may beoptimized by a computer program. The difference between extracted andoptimized values in frequency may then be used to generate a recipe fortuning the filter 900, by for example scribing or trimming one or moretuning element(s). The filter tuning may be implemented by, for example,laser trimming or hand scribing based on the recipe.

Now jumping ahead temporarily to FIGS. 20-22, a technique for takinginto consideration in the tuning procedure a typical exemplary non-idealfilter test environment including the “dirty window(s)” will bedescribed. FIG. 20 shows a physical layout of a typical exemplarynon-ideal filter test environment. In this example, a filter chip 2005is placed in a test housing or package 2010. In the case of an HTSdevice, the housing 2010 will allow the temperature of the filter chip2005 to be cooled to an operating temperature, for example, 77K beforemeasurements of the filter performance are taken. The filter chip 2005housing 2010 may also be used as a real filter device. Filter chip 2005includes a filter 2015 to be tested. The filter chip 2005 usually has 50ohm transmission lines 2030 at both ends that extend the filter's 2015input and output to the edges of the filter chip 2005. The electricallength of the transmission lines 2030 may vary depending on the filter2015 design and its layout. The filter housing or package 2010 may alsoinclude additional transmission line chips 2030. RF connectors 2040 areattached at the sides of the filter housing or package 2010. Those RFconnectors 2040 may be connected with a filter chip 2005 and/ortransmission line chips 2030 by bonding ribbons or wires 2025 and 2035.Those bondings 2025 and 2035 will typically be transitions (ordiscontinuities) far from the desired ideal 50 ohm characteristicimpedance. Often in real world situations, filters 2015 are measured,analyzed and deployed along with these types of unmatched circuits. Insuch situations, the matrix in FIG. 11 may not closely represent thereal situation very well because of the existence of such “dirtywindows” i.e. the non-ideal filter packaging and connection environment.In order to take this non-ideal packaging and connection environmentinto account in the filter tuning analysis, more parameters may beintroduced in the analysis.

As one exemplary way to represent the dirty window characteristics maybe as illustrated in FIG. 21, as a simplified equivalent circuit. Inthis case, the filter chip 2105 is provided with a transmission linefunction 2120A to the left of a filter 2115 and connected thereto, and atransmission line function 2120B to the right of the filter 2115 andconnected thereto, on a chip 2105. Further, using the same left-rightorientation convention, bonding function 2125A is coupled to thetransmission line function 2120A to the left and a bonding function2125B is coupled to transmission line function 2120B to the right. Next,transmission line function 2130A is coupled to bonding function 2125A tothe left and a transmission line function 2130B is coupled to bondingfunction 2125B to the right. Then, bonding function 2135A may be coupledto transmission line function 2130A to the left and bonding function2135B may be coupled to transmission line function 2130B to the right.Finally, connector function 2140A may be coupled to bonding function2135A to the left and connector function 2140 b may be coupled to thebonding function 2135B to the right. Each of these function may beintroduced into the tuning procedure as, for example, a constant,variable or linear or complex function. This additional factorconsideration may help to improve the accuracy of filter tuning.

FIG. 22 is another exemplary simplified circuit representation of FIG.21. By introducing Z_(eff1), θ₁ (DW 2205) and Z_(eff2) and θ₂ (DW 2215)as additional parameters, along with the coupling matrix elements andinput and out couplings (1100), the analysis process will better reflectreal filter devices more accurately and provide better tuning for thefilter devices 2210, including their non-ideal packaging and connectionenvironment. The filter tuning process will now be discussed moreparticularly with reference to tuning filter 900 by returning to theexample shown in FIG. 9, as provided through experimentation.

First, filter 900 was fabricated as an HTS microwave filter fabricatedusing a YBCO thin film deposited and patterned on, for example, a 2-inchMgO wafer. Then filter 900 was put to a typical operating temperature,for example, 77K. A typical operating range for an HTS microwave filtermay be, for example, in a range of approximately 60-100K.

Referring now to FIG. 10, an initial measurement of filter 900 operatingat 77K produced signal 1005. The return loss S11 at an initialmeasurement was about 17 dB and the measured initial filter centerfrequency was about 450 kHz lower than its target center frequency842.37 MHz. Thus, it can be seen that in general the resonators 901-910of the tested device needs to be tuned upward in frequency to achievethe desired pass band and improve return loss.

As noted previously, the tuning process may consist of three primarysteps. The first step is diagnosis of the filter, which may includeparameter extraction. In this example, the measurement data was analyzedby means of parameter extraction technique. Some exemplary parameterextraction techniques are shown in the articles S. Amari, “Synthesis ofcross-coupled resonator filters using an analytical gradient-basedoptimization technique,” IEEE Trans. Microwave Theory & Tech., vol. 48,no. 9, pp. 1559-1564, September 2000 and P. Harscher, R. Vahldieck andS. Amari, Automated filter tuning using generalized low-pass prototypenetworks and gradient-based parameter extraction, IEEE Trans. MicrowaveTheory & Tech., vol. 49, no. 12, pp. 2532-2538, December 2001, which arehereby incorporated by reference for all purposes. A wide variety ofcurve fitting and optimization techniques are known in the art and aregenerally applicable to our invention. For example, The MathWorks Inc.provides a wide array of such routines in their Optimization Toolbox forMATLAB. The specific optimization routines needed will generally dependon the specific filter design. From this information the computerprogram may generate a coupling matrix.

The extracted coupling matrix 1100 is shown in FIG. 11. The solid lineboxes (1105) represent frequency off-set of the resonators, dashed lineboxes (1115) represents main couplings between neighboring resonatorsand dashed and dotted line boxes (1120) represent desired crosscouplings. Those are parameters intentionally designed. Small dottedline boxes (1110) represent parasitic couplings between next neighboringresonators that are not desired to exist (but are nevertheless present).The next-neighboring resonator parasitic couplings (1110) were takenaccount in the extraction shown. In this embodiment, further parasiticcouplings can be ignored because of the particular filter designselected. However, it should be noted that contribution from thosecouplings will generally depend on each particular filter design and mayneed to be taken into consideration sometimes. For example, resonatortopology, arrangement of the resonators, and cross couplingimplementation may all impact parasitic coupling values. Furtherparasitic couplings may have to be included into the coupling matrix asnon-zero elements for some cases depending on design. Those undesiredparasitic coupling matrix elements will generally affect the intendedcross coupling structure. These couplings may impact to filter responseeven though their values are much smaller than main or cross couplingvalues because they create short-cut paths that don't fit in the desiredtopology. It may be worth to point out that existence of parasiticcouplings may make the parameter extraction process more difficult,especially when the coupling structure of the filter design iscomplicated (e.g. multiple cross coupling design) and the resonatorQ-factor is high, such as for filters made with superconductormaterials. The reason is that existence of parasitic coupling mayincreases the number of optimization parameters and also may producesmany local minimum solutions for the optimization. It should also benoted that many filters are packaged in non-ideal microwave packagingand other discontinuities which affect the filter performance as seenthrough the packaging. For example, a microwave filter packaging mayinclude one or more of the following elements that may affect the filterperformance including: microwave discontinuities, transmission lines,microwave cables, bond wires, stripline to microstrip transitions,cryocables, multiplexers, switches, limiters, low noise amplifiers,matching networks, directional couplers, splitters, microwaveconnectors.

The second step of the tuning process is filter response optimizationwhich may include the adjustment of return loss S11. In this case,return loss S11 was optimized in a computer by adjusting resonantfrequencies while keeping the couplings the same with the values thatwere obtained for the filter 900 during the diagnosis step. Since thereal coupling values of the filter 900 may vary slightly from the idealdesign coupling values, and parasitic couplings are present, theresonant frequencies may need to be intentionally mistuned from theirdesign in order to compensate for these undesired coupling variationsand achieve an equalized return loss S. In practice, filter tunertechnicians know this and may intentionally mistune filters to someextent even though they may not know quantitatively by how much.

Referring now to FIG. 12, a graph 1200 of the resulting extractedfrequencies and optimized frequencies for each of the resonators 901-910of the filter shown in FIG. 9 are illustrated. A few exemplary frequencydifferences are as follows. The extracted frequency 1201A of resonator901 is determined to be just less than 840 MHz while the optimizedfrequency 1201B for resonator 901 is determined to be approximately842.25 MHz. The extracted frequency 1205A of resonator 905 is determinedto be approximately 841.2 MHz while the optimized frequency 1205B forresonator 905 is determined to be approximately 842.2 MHz. The extractedfrequency 1210A of resonator 905 is determined to be approximately 841.2MHz while the optimized frequency 1210B for resonator 905 is determinedto be approximately 842.2 MHz. The difference between the extractedfrequency in the first step and the optimized one in the second step maybe translated into a recipe for the physical tuning in the third step.

FIG. 13 is a graph of the initial measured return loss 1305 and theoptimized return loss 1310 for the filter 900 shown in FIG. 9. In thiscase, the computer may generate the optimized return loss signal 1310from the previously performed analysis including the optimizedfrequencies developed for each of the resonators 901-910. The optimizedreturn loss signal 1310 is approximately accurate to produce theexpected of desired return loss at the targeted center frequency of thefilter 900 pass band.

FIG. 14 is a table illustrating the recipe 1400 to be used for tuningresonators 1-10 (901-910) for filter 900 shown in FIG. 9 to produce thetargeted filter response. A row of resonator numbers 1405 and a row ofcorresponding frequency deltas 1410 are provided. For example, byshifting resonant frequencies from a low delta of approximately 673 kHzfor resonator 9 (909) and a high delta of approximately 2322 kHz forresonator 1 (901), the filter 900 will be expected to achieve 20 dBreturn loss at the target center frequency. As can be seen from FIGS. 12and 14, the difference between the extracted and optimized frequenciesis correlated to the amount of frequency shifting required to eachresonator 901-910. This information may be generated by the computer andprovided to a tuning technician as a recipe for purposes of tuning thefilter 900. The tuning recipe 1400 may be, for example, displayed on ascreen or printed on paper.

The filter 900 was then tuned based on the recipe 1400 by hand scribingwith a diamond pen under a microscope. Although, as noted above, othermethods such as laser scribing may be used and the laser scribing may beautomated. FIG. 15 shows a portion of the tuning forks as they werescribed using a diamond pen according to the tuning recipe 1400. Asillustrated, the tuning forks for resonator 7 (907) was tuned byscribing tuning fork 927A at point 1505 between the eighth and ninthscale hash marks and by scribing tuning fork 927B at the fifth scalehash mark. According to the recipe, the seventh resonator R7 needs 742kHz shift for the tuning. The tuning fork 927A is design to give 100 kHzshift by one scale increment and 927B is designed to give 500 kHz shiftby one scale increment. In order to achieve the required shift, 742 kHz,one scale portion of the tuning fork 927B is scribed 1510 for 500 kHzand the location between second scale and the third scale is scribed1505 for another 250 kHz. Since this filter requires 100 kHz resolutionfor tuning on each resonator in order to meet its specification, so thedesign of tuning fork 927A enables scribing between the scales and givesgood enough accuracy for the tuning +/−50 kHz. Further, the tuning forksfor resonator 8 (908) was tuned by scribing tuning fork 928A at point1515 at the seventh scale hash mark and by scribing tuning fork 928B atthe fifth scale hash mark. As with the seventh resonator, one scaleportion of the tuning fork 928B associate with the eighth resonator isscribed 1520 for 500 kHz and three scales portion of the tuning fork928A are scribed 1515 for another 300 kHz.

FIG. 16 shows the tuned response 1610 and the optimized 1605 prediction,after the filter 900 has been scribed according to the tuning recipe1400. The filter is placed again at operating temperature, e.g., 77K,and the filter performance is measure. In this case it is shown in FIG.16 that the band pass filter 900 actual return loss S performance aftertuning 1610 agrees very well with the optimized return loss S 1605 andthus the desired filter performance. This can also be seen in FIG. 17,which shows the filter performance signal 1705 after tuning.

Another embodiment of the present invention is shown in FIGS. 18 and 19.In this embodiment the tuning element may include trimming one of moretabs. FIG. 18 is a top view layout of a multi-resonator planar filterdevice 1800 with trimming tab tuning elements. In this example, tenresonators 1801 through 1810 (1801-1810) are provided in series on asubstrate, similar to previous embodiments. However, in this embodimentthe tuning elements may be one or more trimming tabs, e.g., 1820-1826and 1840-1846. These trimming tabs may be trimmed by severing the tabfrom the resonator, according to a tuning recipe that is generated in amanner similar to that for the previous embodiments. For ease ofunderstanding, FIG. 19 provides an expanded view 1900 of the trimmingtabs 1840-1846 that are shown in the dashed line area 1900 of FIG. 18.

For example, as output of the computer analysis after the optimizationprocess, needed frequency shift for each resonator 1801-1810 may becalculated. Depending on pre-investigated sensitivity of a filter thatis going to be tuned (e.g., the required frequency shift is digitized).Since this example filter may need, for example, 100 kHz precision inorder to meet its specified operating characteristics, frequency off-setmay be digitized in 100 kHz steps. For example, trimming tabs 1840-1846may be designed in binary increment of 100 kHz frequency as a minimumshift. Similar to the tuning fork design, this design may provide foreasy identification of the correct tuning devices to be trimmed. Thisexample is provided with a filter 1800 having seven trimming tabs oneach resonator 1801-1810 that can shift resonant frequency by, forexample, 1500 kHz, 800 kHz, 400 kHz, 200 kHz and 100 kHz. There arethree tabs those can shift 100 kHz. Thus, trimming tab 1840 isdesignated R4-8, indicating that it is associated with resonator 4(1804) and resulting in an 800 kHz frequency shift to resonator 4 whentrimmed. Trimming tab 1841 is designated R4-15, indicating that it isassociated with resonator 4 (1804) and having an 1500 kHz frequencyshift to resonator 4 when trimmed. Trimming tab 1842 is designated R4-4,indicating that it is associated with resonator 4 (1804) and having an400 kHz frequency shift to resonator 4 when trimmed. Trimming tab 1843is designated R4-2, indicating that it is associated with resonator 4(1804) and having an 200 kHz frequency shift to resonator 4 whentrimmed. Trimming tab 1844 is designated R4-1, indicating that it isassociated with resonator 4 (1804) and having an 100 kHz frequency shiftto resonator 4 when trimmed. Trimming tab 1845 is designated R4-1,indicating that it is associated with resonator 4 (1804) and having an100 kHz frequency shift to resonator 4 when trimmed. Trimming tab 1846is designated R4-1, indicating that it is associated with resonator 4(1804) and having an 100 kHz frequency shift to resonator 4 whentrimmed. Thus, using this example, if a resonator such as R4 1804 needsa 670 kHz frequency shift according to a tuning recipe, then, forexample, a 400 kHz tab, a 200 kHz tab and a 100 kHz tab may be trimmed,disconnected, or removed by laser trimming. The process for determiningthe tuning recipe for this embodiment may be the same or similar to oneor more of the processes previously described for the tuning forkembodiments previously described.

Simply rounding the optimized offsets to the discrete tab values canresult in an undesired, (though small) shift in center frequency and anassociated degradation of the filter response. One way to circumventthis problem is to further optimize the discrete tab values. One way todo this is to allow the target frequency to vary from minus half aminimum tab step to plus half a minimum tab step, i.e. −50 to +50 kHzfor a minimum tab step of 100 kHz. In this way there will be a finitefamily of discrete tuning states that will each be a set of the tabs tobe trimmed. The set of tabs to be trimmed can then be chosen from thisset of tuning states by examining a number of characteristics of thetuning state. First, the average remaining offset between the discretetuning state and the optimized frequency offsets can be attempted to beminimized, as this will contribute to the ultimate frequency offset.Second, one can also attempt to minimize the sum of squares of theseremainders to determine the discrete tuning state that best representsthe optimized frequency offsets. Third, one can examine the filterperformance (e.g. return loss S11) for the family of discrete tuningstates and select the tuning state which yields the closest to thedesired performance. Fourth one can examine the stability of a giventuning state, by examining the frequency width over which it describesthe optimized frequency offsets, as this will tend to give a more robustsolution.

While embodiments of the invention have been described above, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. For example, other methods ofremoval of material could be considered beyond laser or diamond penscribing for either tuning fork or trimming tab type tuning elements,including but not limited to standard wet or dry photolithographictechniques, or focused ion beams (FIB). In another variation of theinvention, the tuning element may be an electronically variablecapacitor such as a semiconductor varactor, switched capacitor bank orMEMS capacitor. Any of the methods described for resonator tuning thatare described in U.S. Pat. No. 6,898,450 “High TemperatureSuperconducting Tunable Filter”, U.S. Pat. No. 6,727,702 “TunableSuperconducting Resonator and Methods of Tuning Thereof” and U.S. patentapplication Ser. No. 10/162,531 “Varactor Tuning for a Narrow BandFilter” could be used in conjunction with this invention and thesereferences are incorporated herein for all purposes. Accordingly, theembodiments of the invention, as set forth above, are intended to beillustrative, and should not be construed as limitations on the scope ofthe invention. Various changes may be made without departing from thespirit and scope of the invention. Accordingly, the scope of the presentinvention should be determined not by the embodiments illustrated above,but by the claims appended hereto and their legal equivalents.

1. A method, comprising: providing a filter including at least one resonator(s) and at least one tuning element(s), said filter having one or more filter design parameters selected from a group that includes resonator frequencies and resonator to resonator coupling values; measuring a response of said filter so as to generate a set of measured data including at least a first set of measured data and a second set of measured data; analyzing the set of measured data to extract one or more filter design parameter(s) to optimize, and the analyzing is done utilizing additional parameters representing a non-ideal filter environment, the first set of measured data and the second set of measured data; optimizing a selected subset of filter design parameters to achieve a desired filter response; generating a tuning recipe for an operator or automated tuning system to use in tuning the filter; tuning the filter by altering the at least one tuning elements as established by the tuning recipe so as to correspond to said subset of filter design parameters; and packaging the filter for use without confirming performance.
 2. The method of claim 1, wherein the filter is planar, the at least one tuning element(s) is a separate structure from a structure of the at least one resonator(s), and both the structure of the at least one tuning element(s) and the structure of the at least one resonator(s) are formed on the same substrate.
 3. The method of claim 1, wherein testing for and generating the tuning recipe occurs only once and the tuning recipe is used for making a plurality of adjustments to the at least one tuning element(s).
 4. The method of claim 3, wherein the filter is made of a superconducting material or a high temperature superconductor (HTS).
 5. The method of claim 1, wherein the filter response measurement is carried out at a standard operating temperature of the filter and the tuning of the at least one tuning element(s) is carried out at a temperature that is not an expected operating temperature of the filter.
 6. The method of claim 1, wherein the set of measured data consists of more than one measurement of the filter response of the filter and the filter has been subjected to a known modification by altering one or more of the at least one tuning element(s) before at least one of the more than one measurement.
 7. The method of claim 6, wherein the known modification is adjusting the resonant frequency of at least one resonator at an ambient temperature.
 8. The method of claim 1, wherein the filter has more than four resonators and includes cross coupling elements between non-adjacent resonators.
 9. The method of claim 1, wherein tuning is realized by removal of material at a temperature that is not an expected operating temperature so as to modify a capacitance or inductance in the filter by a known amount as indicated by the tuning recipe.
 10. The method of claim 1, wherein tuning is realized by removal of material is achieved by means of a laser, diamond scribe, focused ion beams or photolithography performed at a temperature that is not an expected operating temperature of the filter.
 11. The method of claim 1, wherein the at least one tuning element(s) is formed on the same substrate as the filter and includes one or more tabs which can be removed to reduce a shunt capacitance in the circuit.
 12. The method of claim 1, wherein the at least one tuning element(s) is formed on the same substrate as the filter and consists of an array of tabs whose size and position are set so as to provide a binary array of shunt capacitive elements of varying sizes defining a tuning range and a minimum tuning resolution.
 13. The method of claim 1, wherein the at least one tuning element(s) includes one or more tuning forks which are capacitively coupled to the filter.
 14. The method of claim 1, wherein the at least one tuning element(s) include predefined gauged locations for altering the at least one tuning element(s).
 15. The method of claim 1, wherein the optimized parameters are further optimized to account for a minimum realizable parameter change achievable with the at least one tuning element(s).
 16. A filter tuning apparatus, comprising: a detuned multi cross-coupled resonator filter comprising more than four resonators including cross coupling elements between non-adjacent resonators, each resonator having at least one tuning element; a filter response measurement device; a first set of measured data; a means of adjusting the tuning element so as to achieve a change in one or more known filter design parameter(s) of the filter; a second set of measured data obtained after the tuning element has changed one of the one or more known filter design parameter(s); a means of extracting filter design parameters utilizing additional parameters representing a non-ideal filter environment, the first set of measured data and the second set of measured data in view of a change in one or more known design parameter(s); a means for directing the means of adjusting the tuning elements so as to achieve a desired filter performance based on extracted filter design parameters, and wherein the at least one resonator and the corresponding at least one tuning element are separate structures such that the corresponding at least one tuning element is designed specifically and uniquely to help tune the filter more easily, and not part of the resonator structure; and non-ideal filter packaging and other discontinuities which affect the filter performance as seen through the non-ideal packaging and other discontinuities.
 17. The filter tuning apparatus of claim 16, wherein the directing includes a tuning recipe used in adjusting the at least one tuning element.
 18. The filter tuning apparatus of claim 16, wherein the tuning elements include predefined gauged locations for altering the at least one tuning elements. 